BM5, a mixture of retroviruses induces a fatal immunodeficiency syndrome when injected into C57BL/6 mice. The most interesting feature of this disease is an absolute requirement for CD4 T cells for disease induction and progression. Interestingly, as the disease sets in, CD4 T cells become completely unresponsive to polyclonal and antigen-specific stimulations. Moreover, BM5 retroviral mixture appears to either encode or stimulate an endogenous superantigen which deletes Vbeta5.2 positive CD4 T cells in the spleen and lymph nodes of infected animals. This model presents an ideal in vivo system to study CD4 T cells that are rendered anergic by retroviral infection because entire CD4 T cell population representing various Vbeta TCRs is anergic and is not restricted to a few subsets of CD4 T cells. We will take advantage of such a system to.study the process of anergy as CD4 T cells steadily lose their capacity to proliferate or synthesize cytokines in response to various stimuli. The initial approach is to pinpoint the defective steps in the cascade of reactions that follow TCR stimulation. We will test the possibility that there is an altered tyrosine phosphorylation of substrates since it is the first step in signal transduction and the involvement of tyrosine kinases such as p56 1ck, p59 fyn and phosphatases like CD45 in anergy. Other steps in signal transduction namely, phosphoinositide hydrolysis and subsequent CA++ release and activation of PKC will be evaluated. Next, we will monitor the expression of various costimulatory molecules on anergic and normal CD4 T cells. In order to assess the role of costimulatory molecules in inducing lymphokine gene expression, we will coculture anergic CD4 T cells with anti-CD28 or provide APCs that have high expression of B7 and study the effects on IL-2 and IL-4 gene transcription. In most superantigen induced anergy systems, anergic cells undergo apoptosis when they are stimulated via the TCR. Apoptosis is blocked in cells with elevated expression of bcl- 2 and is induced in cells with high c-myc expression. These observations suggest that protooncogenes such as bcl-2 and c-myc have a major role in maintaining anergic cells in vivo. We plan to study the expression of bcl-2 and c-myc in anergic CD4 T cells and their role in maintaining anergic CD4 T cells in vivo. We believe a model system like BM5 retrovirus induced CD4 anergy will enable us to design experiments to follow the course of CD4 T cells as they progressively expand in vivo, yet fail to function and become anergic. This system is well suited to study the biochemical events involved in signal transduction, costimulation and finally apoptosis of anergic CD4 T cells.